Method and apparatus for determining surface of comminuted material



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SECONDS POROS/TY Patented Jan. 8,

METHOD AND APPARATUS FOR DETERMIN- SURFACE OF COMMINUTED MATE- Robert E. Boehler, Gary, ma, assignor to Umfirsal Atlas Cement Company, a corporation of Application December 21, 1942, Serial No. 469,710

v duce a mortar of a given strength.

8 Claims.

In the production of powdered materials, such as cement, importance may be attached to the degree of fineness of grinding of the material, since, in the case of cement, there is a direct relation between the fineness of the cement particles and the setting-properties of the cement.

'Ihus, it is generally accepted that the coarser particles in cement are practically inert, and it is only the extremely fine powder that possesses adhesive or cementing qualities. The more finely cement is pulverized, all other conditions being the same, the more sand it will carry and pro- In the early stages, of hardening ,of cement,

, only the finer particles have any effect, as water is slowin reaching the interior of the larger particles, thereby delaying the hydraulic action. Also, the finer particles more easily cover the sand, grains, making mortar much stronger, and allowing use'of larger percentages of sand. Also seasoning can take place more easily with finely ground cement; because of this, fine cement is less liable to unsoundness.

In view of the importance of grinding of cer-,

tain powders, such as cement, it becomes necessary to make frequent tests, on the material dressing the grinding process in order to effect requisite adjustments of the mills in the event that through some cause, the mill is not performing satisfactorily. In view of the fact that such tests should be made frequently during the A grinding, it is necessary that they be done in an expeditious manner as the grinding proceeds.

In accordance with the present invention, there are provided a new process and apparatus for determining the fineness of materials such as cement, or for that matter, virtually any comminuted substance that, for any reason, may be desired to be tested for fineness, cement being the illustrative embodiment of the invention which is illustratedand'described herein.

A further object of the invention is to provide a method and apparatus which combines speedwith sufllcient ruggedness of 'mechanical construction to enable the equipment to be installed immediately adjacent to a grinding mill, for quickly making determinations for effecting required regulation of thegrinding operation. A still further object of the invention is to provide testing equipment which is suitable for use by a person such as a mill operative, and not necessarily by a trained laboratory technician and which eliminates the use of delicate laboratory apparatus.

It may be mentioned in this connection that a still further object of the invention may be stated to be the provision of equipment on which there may be taken direct readings in terms of surface,

thereby avoiding the necessity for calculations.

. The present invention is based upon the fact that fineness of the particles is measured by determining the total surface presented by a standard'bed of the powder, as determined by pressures required to force a penetrating fluid, such as air,

10 through such standard bed, and reading the results in terms of surface. g

This is, accomplished on the. basis of the Caiman equation for determining'surface by the permeability ofliquids through beds of granules. In

the present invention, instead of forcing a liquid through standard beds, air is used as the per meating fluid, and as the density of air is expressed in terms relative to the density of fluids,

be relative.

P. C. Carman (Journal of the Society of Chemical Industry, vol. 5'7, 1938, page 225; and vol. 58, .1939, page 227) derived the principles involved, and the present invention embraces the method, and inseparately therefrom, the calculations that are involved, together with a compact apparatus for carrying out the method as stated above, the invention being predicated upon the relations expressed by the aforesaid Carman equation for determining surface by the permeability of liquids through beds of granules. When air is used as the permeating medium, and its density is expressed in terms relative to the density of fluids, the fineness also may be assumed to be relative.

In the Carman equation, the variables affecting specific surface are porosity, kinematic viscosity and permeability. 'Ifheir relation of each other is as follows:

DETERMINATION or SPECIFIC SURFACE BY APPLICA- TION or CAnMANs EQUATION TO THE BOEHLER SINGLE MANOMETER SURFACE METER The following considerations explain the meth- 0d and calculations involved in determining the fineness of materials in terms of square centimeters per gram, with the single manometer air surface meter of the present invention.

The following calculations ar based upon the Carman equation for determining surface by the permeability of liquids through beds of granules. When air is used as the permeating'medium and its density is expressed in termsv relative to the density of fluids, we assume the finenessalso to be relative. In the Carman equation, the variables affecting the fineness of the granules also is assumed to specific surface are porosity, kinematic viscosity, and permeability. Their relation to each other is as follows:

The specific surface may also be expressed in sq. cm. per gram by dividing both sides of the equation by the density of the material. The constants g and k may be combined and removed from under the radical sign, giving the equation as follows:

d d KV(1 E) where d=density of the material In the development of the present invention, it was necessary to examine each of the variables and apply them appropriately to the instrument of the present invention. Th following description shows the method used in determining:

1. Average or meaneifectivepressure 2. Total volume of the air system.

3. Volume of air passing through sample 4. The porosity factor E 5. The kinematic viscosity factor V 6. The permeability factor K 7. Apparent linear velocity 8 Unit hydraulic gradient 9. Surface-porosity correction number 2 Since the air pressure is constantly changing as a surface test is being made, it is nececssary to find the average or mean-efiective-pressure in order to determine the unit pressure gradient which enters into the valve for permeability, and th air density which enters into the valve for kinematic viscosity.

As used in this article, the mean-effective-pressure is that valve of pressure which, if held constant, would pass the same volume of air through the sample in the same interval of time.

THE MEAN-EFFECTIVE Pnrzssoxr.

Time measurements were taken as the pressure decreased and the readings tabulated in Table 1 below.

The logarithms of pressure were plotted against the total time in Fig. 9 of the accompanying drawings referred to hereinafter, and the approximate straight line indicated that the relation between pressure and time could be approximately represented by:

The mean-eflective-pressure acting between points Pa and P1. is found by determining the area below the curve between the limits Pa and P1. and dividing by the time interval between these points.

The area= H H M H P H 59 s: I: Pdt Lee a L L Then mean-efiective pressure= Pg- P b log Pg-lOg P ==b log 6 (t -1 Of b-log Pg-log P ea-1,. 10g 5 (3) Substituting (3) in (2) Mean-efiective pressure:

P -PL (t -t log 41 (Pg-'P log e (t -Q) log Pg-l0g P log Pg-lOg P Mean-effective pressure= P -P 4 log PH-m P (4) Table 1 Pressure Average Observed Cumulative Log. of ave. drops pressure time observed time press.

29-28 28. 5 7. s 7. 8 1. 4549 28-27 27. 6 a. 4 16. 2 1. 4891 27-20 26. 5 8. 8 25.0 1. 4234 26-25 25. 5 8. 6 as. 6 1. 4065 25-24 24. 5 10. 6 44. 2 1. 3590 24-23 23. 5 9. 6 53. 8 1. 3710 23-22 22. 5 10. 6 64. 4 1. 3522 22-21 21.5 10. s 75. 2 1. 3324 21-20 20.5 12.4 87.6 1.3119 20-19 19.5 11.4 99.0 1.2900 19-18 18. 5 14. 4 113. 4 1.2673 18-17 17. 5 14. 0 127. 4 1. 2461 17-16 16. 5 14.6 142. 0 1. 2174 16-15 15. 5 17. 0 159.0 1.1903 15-14 14. 5 17.8 176. 8 1.1614 14-18 13. 5 19. 6 196. 4 1. 1305 13-12 12. 5 20. 6 217. 0 1. 0971 12-11 11.5 21.8 238. s 1. 0661 11-10 10.5 25. 6 264. 4 1. 0258 10- 9 9.5 28.0 292.4 0.9780

FINDING TOTAL VOLUME OF THE AIR SYSTEM The total volume of the air system is calculated by determining the time it takes the mercury column todrop from point H to point L with and without a displacement plug of known volume inserted into the air system by using the same sample for both tests as follows:

where T =time of drop without displacement plug. T =t1me of drop with displacement plug. V1=fotal volume of air system.

V3=V01l1mB of displacement plug.

then

'Pr-T3=tlm8 difl'erence representing the eflect of laci th into the system. p Hg a plug 2 -14516 of total volume to plug volume. hence Since the total volume of the system is changing by a small amount as the mercury drops from -AL==totai volumeof the bed.

i to L. due to the mercury in the columm'the calculated totalvolume is apparently the volume when the mercury is midway between H and L.

It is possible to increase accuracy in finding the volume of the air system if a'large portion of the total volume is displaced. Provision has been made in the design of the air chamber to\- permit mercury or water-of known volume to be admitted to the air system instead of a-displacement plug; By this means more than half of the total volume may be displaced.

Vomnn: or AmPAssnm Tnnoucrr Bum: Knowing the total volume of the air system (V1) the volume of free air passing through the sample when the pressure drops from point H to point L can be calculated as follows:

P =absolute pressure at point H I P =the barometric pressure then 11 the number of atmospheres above absolute zero contained in the air system at point H Let total volume of free air contained in the air system at point H and then -volum'e occupied by solid particles.

AL-==volume of voids.

By using the same cell on all tests, and by} assigning proper weights of sample for the ranges P P proportionate part of total drop available 8 which is used in testing Therefore, the total volume of free air contained in the system at point H multiplied by the proportionate part of total pressure drop available which is used in testing will equal the volume of air passing through the sample when testing.

where V volume of air passing through the sample since P =P +P the formula can be reduced to I'm; POROSITY Fscroa E w=weight of sample, in grams.

d=density of material, in grams/cu. cm. A=area of cross-section of cell, in sq. cm. L=length of cell occupied by sample, in cm.

of surface of the varlousgmaterials to be tested,

w, A, and L will-be constants and the Porosity factor can be brought down'to containone variable, the density, which must be carried to the final equation for surface. It has been found that when the density varies slightly, the surface results change considerably.

It was also found that as the porosity was lowered, within a certain range, the unit surface, as calculated by Carman's Equation, increased while using the same material.

Investigation of the curves obtained from various samples of known surfaces led to the determination of correction exponents designated as :c in Figure 12 of-the accompanying drawings.

For the purpose of shortening the calculations,

the same relation was maintained by retaining the Carman exponent of 3, and substituting'the correction number designated as a in Figure 13 of the accompanying drawings; both of which view's will be referred to in detail hereinafter.

It was also found that the amount of increase in surface, as mentioned above, is greater with higher surfaces. Therefore, the correction exponent, and the correction number, change depending upon the surface.

Further, it was found that the porosity must be low enough to prevent the possibility of having a greater air pressure at point T on the manometer than the pressure used in compressing the sample. Figure 13 shows the upper limits of porosity permissible for various surface ranges with this instrument.

Tna'Kmsmarrc Vrscosrrr Fscros V By definition, the kinematic viscosity is the ratio of the absolute viscosity to the density'of the fluid.

or V= Where V=kinematic viscosity in sq.- cur/sec,

n=absolute viscosity in grams/cm./sec. P=density of the fluid (air) in grams/cu. cm.

From Figure 11 of the accompanying drawings, the absolute viscosity corresponding to the existing room temperature may be found directly.

Figure 10 of the accompanying drawings shows the density of air at 76 cm. of mercury; Since the pressure, and therefore the density of air is not constant as it passes through the sample, the average density is therefore based upon one-half of the mean-effective pressure across the sample. As the mean-efiective-pressure was calculated for gage pressureand air density is a function of ab- Obviously, the porosity exponent of 3 does not hold constant.

solute pressure, correction can be made by using the factor Pe=mean-eflective-pressure .in cm. of mercury. Ps=barometric pressure in cm. of mercury.

where P' is the value taken from Figure 9.

THE PERMEABILTIY FACTOR K The permeability factor is the ratio of the apparent linear velocity of the fluid (air) to the unit hydraulic gradient across the bed.

" Considering first the apparent linear velocity:

Apparent linear velocity:

vol. of air passing seconds required cross-sectional area For any one instrument, the volume of air passing will be constant when the points H and L on the manometer are fixed and there are no great variations in the barometric pressure. The cross-sectional area of the bed is constant as determined by the physical dimensions of the cell used. Time is the variable,and when a cycle counter is used for its measurement, the frequency constant must be introduced in converting seconds to cycles.

The unit hydraulic gradient is the pressure drop per unit length of the bed. Since the sample is compressed to the same thickness before each test, the depth or length of the bed is a constant. The pressure drop across the bed is the mean-efiective-pressure previously determined.

Hence,

Unit hydraulic gradient=% where Pe=mean-effective-pressure in grams/sq. cm.

and

L=depth a bed in cm.

Thus

volume of air passing time required cross-sectional area of bed mean-eifective-pressure depth of bed g 1 volume of airpassingX depth of bed mean-elfective-pressureXarea of bedXtime required P0 K PH.-PL V,L

PTPT 1z a It will be found in supplying the numerical values that K can be reduced to a constant i 'z H The German equation as applied to the apparatus of the present inventionnow becomes:

where d=density of the material, in grams per cu. cm.

=weight of sample, in grams.

A=cross-sectional area of bed, in sq. cm.

L=depth of bed, in cm.

t=time, in seconds, for mercury drop from H to L.

Pa==mean-eflective-pressure in grams per sq cm.

P=density or the permeating fluid (air).

V4=volume of air passing through the sample, in

cu. cm. n=absolute viscosity of the air, in grams per cm.

per sec.

Other symbols referred to herein are the following:

Pa=barometric pressure, in cm. of mercury.

Pn=gage pressure at point H, in cm. of mercury.

PL=gage pressure at point L, in cm. of mercury. Pc=mean-efiective-pressure in cm. of mercury.

P1=absolute pressure at point H.

40 V1=total volume of the air system, in cu. cm.

CALIBRATION OF THE INSTRUMENT The height of the mercury column at point H was 98.08 cm, and at point L, 51.08 cm. These measurements were obtained after making allowance for the change in level in the mercury pot due to change in the height of the column, and the volume displaced by the wires for the cyclecounter contacts.

- Mean-efi'ective-pressure:

H- P1. log P log P Therefore P=fi8.58 cm. of mercury.

and

Pa=68.58 13.59=932 grams/sq. cm.

The constants for the permeability cell are:

A=9 sq. cm. L=5 cm.

In determining the total volume of the air sys-' tem, several displacement plugs, machined from ,of the set screws were calculated from their weights and density, and added to the volumes for the respective displacement plugs. Choosing three plugs having the greatest relative differences in volume, and taking time readings as the mercury dropped from point Hto an arbitrary point about 6 inches above the mercury pot, first without the plug, and then with the plug, the

total volume of the air system was found from the average of the readings and the known volumes oi the respective plugs. The point about 6 inches above the pot was selected in order to lengthen the time and reduce the errors in readings. The cycle counter was used as a check against the stop-watch results. As developed,

the volume of the air system was found from Using a 72 gram sample of Standard Portland cement having a density of 3.135 grams per cu. cm., the time of mercury drop from H to L was 1809.1 cycles. For this sample l; l dAL s.135 9 5 9.75 9.75 cycles 1809.1 00539 This sample was, known to be in the 4000 air surface range. From Figure 13, the correction number afor this range and porosity is .9862.

1 Volume of air T1 T: -T {1T Ki &1; a 'v l 0:3345 1 0 l a 3 I71: V1 535.7 0. C.

2294.1 2137.7 14.55 911.9244 541.7 1.12 g f ig 2294.1 2177.11 19.70 27. 2996 537.5 0.53?!- 2294.1 2170.0 18.50 28.9752 535.9v 0. 0374+ S t o D 192.0 123.35 14.94 36.9344 530.0 1.075-

watch 132.6 120.15 20.55 27. 29911 551.0 4. 73+

Average 539. 9 Total 4. 7364+ Average without 561.0 535. 7 Total 0. 0064+ These results indicate the volume ofthe air Hence system to be very nearly 536. cu. cm.=V1. 14 2 14 E E Knowing the volume of the air system, the Sm= -X g gage pressures at points H and L, and the barometric pressure, the .volume of air passing 14 489644896 1 through the sample can be found by the method 3,145

developed as afore-mentioned, i. e.

P 'P 89.08-51.08 P, 74.68 536 V. =272.7 cu. cm.

The permeability factor K referred to in foregoing equations becomes:

(s9.0s-51.os)53c 5 .1525 74.68 X 932 X 9 X seconds seconds 9.75 cycles (for 60 cycles/sec.)

KINEMATIC VISCOSITY -12.015 10 grams/cu. cm. at 76 cm. of mercury. The barometer reading was 74.68 cm. of

mercury. From Figure 11, the absolute viscosity of air at 70 F. is .00000018605 or 18.605 10-- grams per cm. per sec.

.9862--.4896 .00539X.0001082 =4025 sq. cm./gram Under the same conditions but replacing the same cement, we have and t=2539.8 cycles By the method. as shown previously, Sw=4036 SPECIFIC GRAVITY Regardless of what is done with the instrument to obtain precision, the results accomplished regarding surface are only approximate unless the density" of the sample is known. Tests have shown that a given standard cement varies from 3.06 to 3.15.

'In the Carman equation, the density is used in three places, and a change of 1% in density gives a corresponding change of approximately Specific gravity by centrifuge method Two samples of 175 grams each are vibrated into heavy glass bottles containing enough fluid to cover the samples; The bottles are then balanced by adding fluid and placed in the centrifuge for one minute to drive out the entrained air and compact the samples to an extremely dense state. The volume occupied by the sample is found by determining the volume of fluid which the sample displaces. This can be done quickly by taking from a prepared graph, the weight of fluid for the full bottle at the prevailing temperature, and deducting the net weightof fluid which was added above the sample to fill the bottle. From another graph of temperature, weight and volume, the volume of the sample is found from the weight of the displaced fluid. Then, the ratio of 175 to the volume just found, is the density of the sample.

STANDARDIZATION OF INSTRUMENTS In the construction of a number of instruments it is to be expected that their total volumes will vary. Nevertheless, it is possible to keep the mean-effective-pressure and the volume of air passing the sample the same for all instruments by properly locating points H and L. When this is done, all instruments will have identical characteristics.

A practical method of locating points H and L to maintain the required volume of air passing the sample, is by making use of the approximately linear function, throughout the normal operating range, of log P versus total time. As the total volume varies directly as the total time, the logs of PH and P1. can be established by dividing this total time equally across the point of log Po, the standard mean-effective-pressure.

From the calibration of the first instrument, we have:

Pc=mean-efi'ective pressure. V1=total volume of the air system. Pn=pressure at point H. Pn=pressure at point L.

and assuming linear relation we have:

log P,

solving for log PH" 2 log Pc= Pn-l-log P1. 2 log Pc=2 log Pn+logP1..-log Pa 2 log Pn= 2 Iog P+log PH-lOg Pr.

V (log P -log Pl.) logy P log P,+ and by the same method:

I log PL=1og P YL l- L Vr(log Pia-log PL) :0, a constant (3) Substituting (3) 111(1) and (2) we have 0 log P =log Pal-m and 10g P =10g Pg- If 4 V1=volume of air system of a second instrument Pn'=pressure at point H of .a second instrument Pr.'=pressure at point L of a second instrument 1 2 ies i) 10g PH'-10g and 1 8 H" g PL) 10g PL'-10g P '-V17 2' PH=89.08 log PH= 1.9497 PL=5L08 10g PL=1.7082 Pc=68.58 log Pc=1.8358 V=536 1 then 536( 1.9497- 1.7082) I log Pg 1.9497+ VI,X2

129.444 log P =l.9497+ and 129.444 log P,,=1.9497

APPLICATION '1'0 MILL CONTROL and C: (secondsaaeac where Approximate surface results may then be obtained by taking the product of the timer dial reading and the instrument constant.

If it should seem desirable to assume a con-- stant density of material, the timer dial may be graduated inspecific surface, giving a direct reading instrument of sufficient accuracy for mill control.

- CALIBRATION or rm: INSTRUMENT r rm: WAGNER Tunarnmn'rsa Using two 72-gram samples having reasonably well spread values of Wagner surface, the time required for each sample in the air surface meter is taken. Since the square root of the seconds is a straight line function to surface, a graph of Wagner surface vs. square root of seconds can be constructed using the two coordinate points to determine the slope of the line. The square root of seconds corresponding to the cardinal points of Wagner surface can be taken from the graph. Figure 14 is an example of such a graph.

By squaring the values of square root of seconds, a curve can be constructed for seconds vs. Wagner surface, as shown in Figure 15. From this curve a surface scale can be placed on the timer dial to indicate Wagner surface directly.

With reference to the foregoing, attention is called to the accompanying drawings, wherein:

Figure 1 represents a side elevation of an apparatus for practicing the method of the present invention.

Figure 2 is a sectional elevation of the sample.- receiving cylinder, showing a sample of powder introduced therein.

Figure 3 is a sectional elevation showing the first step of preparing the sample.

Figure 4 is a sectional elevation showing completion of preparation of the sample.

Figure 5 is a sectional elevation of the sample mounted in the test frame for testing,

Figure 6 is a sectional elevation showing a method of removing the sample from the cylinder.

Fig. '7 is. an enlarged diagrammatic view of the manometer equipment embracing the principles.

Figure 8 is a view of the apparatus of'Fi'gure l rendered portable.

Figure 9 is a graph obtained by plotting logarithms of pressure against'total time.

' between different air surfaces and porosity.

Figure 15 is a graph showing the relationship between the square root of the times and the surface values obtained by the use of the Wagner Turbidimeter.

Figure 16 is a graph showing the relationship between the time in seconds and surface values as obtained from the Wagner Turbidimeter,

Referring more particularly to the drawings, and first to Figures 1 to 5 inclusive, a sample of powder to be tested which has been indicated at 8 is introduced into a cylindrical cup l0, placed at a sample-filling station A on a table II, through a funnel i2 orother suitable introducing means. The cup I0 is adapted to sit on table II .and is provided with a perforated bottom H, the perforations being covered with a layer of filter paper or fine-meshed cloth for retaining the powder, this being indicated at 18. The bottom l4 preferably is made removable by forming it as a part of a bracket l8 which is threaded into the bottom portion of the sleeve, as is indicated by threads 20. As is shown in Figure 3, the table II is pro vided with a suction station B which is immediately adjacent to the sample-filling station. The suction station includes a suction line 22, which opens at the top of table II through a suitably apertured fitting 24', the top of which fitting forms a plate 25 having a hole 21 therethrough, the plate 25 being adapted to receive the cylinder l0 with the hole 21 in communication with the interior of the cylinder for evacuation thereof. i i

The cylinder l0, containing the powder sample 8, is fitted with a piston plug 26, which is milled so as to have a close sliding fit in the cylinder. The piston plug 26 has an enlarged head 28 which forms an annular shoulder 30 adapted to seat on the' end of the cylinder l0 when the powder sample 8 is compressed fully.

The suction station B is located immediately adjacent to the station A and the cylinder l0 with .the piston plug 26 and sample 8 therein mobility of the solid particles produces flow thereof from the cylinder wall downwardly and towards the center, and all layers from bottom to top represent as nearly uniform packing as can 'be attained at this stage. The sample so compacted remains as a cylinder slightly less in diameter than its metal container, its upper surface under the piston plug being'slightly higher than required.

Consequently, in order to finish compacting, the cylinder I0 with its contained partially compressed sample and piston plug, is moved to a compression station C where a screw 32, operated by crank lever 34 is caused to press upon the piston head 28 in recess 36 provided therein for this purpose until the shoulder 30 is forced into engagement with the cylinder l0, thereby completely compressing the sample for the purpose of this invention.

Before applying pressure from the screw 32, the cylinder of powder is not in contact with the walls of the metal cylinder Hi, the powder particle have some freedom of movement under pressure until restrained by the metal wall. The powder appears to have some further degree of compressibility, so that, for instance among cement samples varying enough in fineness and specific gravity to afiect the bulking tendency, it is possible to compress a standard weight withtom 40.

in the-length allowed. It is conceivable that,

with great pressure, enough packing could be developed as to. impair the porosity of the bed so that the calculated value and the values obtained by direct observation would not represent the true porosity of the bed. Adiustment of the weight o-f the sample and degree of mechanical pressure is a matter for experiment not concerned with the present invention, which provides a means for compacting the sample into an accurately dimensioned cylinder in such con-- dition as to satisfy requirements for the test.

The cylinder I with its sample thus compacted, then is removed from the press '0 and placed in testing frame D.

This frame is fastened to the table II immediately adjacent to the press C, and includes a frame having sides 35, 36', a top 38 and a bot- -The sides 36, 36' are bolted suitably to the table II by bolts 42, and the top 38 also is secured suitably, such as by screws. The top 40 has a hole 45 extending through it, into which hole is inserted snugly a pipe 48 which joins compressed air line 50.

A..;Iunction i connects pipe 48 with a branch pipe 52, this branch pipe opening under a piston head 54 positioned in a cylinder 55 mounted on the side frame members 36, 36'.

The piston head 54 actuates a piston rod 58, which is shown as extending through a hole 80 suitably provided therefor in table II. A washer 62 is provided adjacent to the bottom end of the piston rod 58, and a cushioning coil spring E4 is retained around the rod 58 between washer .Pipe 50 is connected to a source of compressed air which is controlled by a valve 82, there being also a pressure chamber 84 in the line 50; and a pressure gage 86 also is in the line 50.

It will be understood that the powder sample 8 is of standard weight, and when properly compressed, as described above herein, the pressure which is required to force air through such standard bed is the value which, in accordance with the present invention, is to be measured.

Consequently, when the cylinder I0 is placed in the test frame and the valve 82 is opened, air flows through the pipes 50 and 52 beneath the piston head- 54 to lift the 'bottom against the cylinder I0, thereby tightly holding the cylinder I0 between the bottom 40 and the top 38. Air-tight ple, escaping from chamber 94 beneath the sample to the atmosphere through pipe 12. Pressure rises in the space 96 above the sample, this pressure rising to' as much as 50 lbs. per square inch. Pipe 50 is connected to pipe 98 which opens into aaeacer well I00, in which is mounted a manometer tube I02, containing contacts I04, I06 (Figure '1) contact I08 being theshortcr, and terminating at a point H, the longer contact I04 terminating at a point L.

An electric clock I08 having a self-starting motor I09, (for example a motor of l-R. P. M.) pointer H0, and dial H2, is provided. The clock motor I09 receives current from an alternating current supply line H8, I20, and is operative through the medium of a self-holding circuit including a relay coil I22 having a core I24 which carries contact arms I26, I 28 and I30, arms I26 and I30 being connected at contacts I26 and I30 to leads I 3.2 and I34 of the clock motor.

Gage contact I 08 is connected through lead I35 to a relay coil I38, the core I40 of which carries contact arms I42, I44. A condenser I46 is connected across the coil I38, the coil I 38 being connected to coil I22 through a lead I40 and to gage contact I04 through lead I50, in which is connected a condenser I 52.

Switch arms I42, I44 are adapted to make and break engagement with the pairs of contacts I54,

' I56 and I58, 5%, respectively, while the motor switch arms I26, I28 and I36 are adapted to make and break engagement with contacts I62, I 54, I58, I58, no, and H2. Of these, contact I 66 is merely a stop, and is not electrified.

Contact 556 is connected to power. lin lit through lead Ht. Contact I56 is connected to contact set through lead I76. Also contact I52 is connected through lead IIE to the direct current line I I6, contact I58 being connected through lead I88, to lead I82, which connects the solenoid coil I 22 to contact I58. Contact H0 is connected through lead I84 to a suitable point I861), on resistance I85 which is connected across the conductors H4 and lit, the adjustable contact of which resistance is connected, at point IBM, to lead I 48- through lead I 38, the end of resistance I85 being connected to the mercury well I00 through lead I90. Contact ltd is connected to lead I68 through lead I 92.

Power supply lines t, H6 supply direct current to the relay coils as well as to stop the motor I09 instantly when contact is broken at point L. This direct current applies a dynamic brake to the clock motor. This current supply is, for instance, volt. D. C.

Current from the line II 8-120 suitably may be a 60-cycle alternating current for driving the motor I09.

Th condensers I46, I52 eliminate arcing when the mercury breaks contact at points H and L.

The relay are reset automatically for operations when contact is made at point H asthe mercury is raisedin the manometer.

The relay I38 is a two-pole type, with one contact normally open and one normally closed, while contact relay I22 is a triple pole double throw type of relay.

When the operation of the device is as follows:

When the valve 82 is opened, air enters the pipe 50 and raises the mercury in the well I00 to a certain level, such as the point T, which is constant under the pressure of the air in the pipe 56. This point is usually, in practice, about 30 inches high.

A the mercury is raised in the tube I 02, a circuit is established through lead I36 and coil I38 which closes the-contacts I58, I60 and opens I54 and I56.

Whencontacts I 58I60 close, current is established through lead I48 through relay coil' I22, to close this relay.

This action causes an alternating current cirasoaeav A v In the present apparatus, the pressure varies,

cult to be completed by pulling arm I28 from contact I82 into engagement with contact I88, arm I28 from the stop I88 into engagement with contact I88, and arm I88 from contact I12 into engagement with contact I'll, thus setting the clock motor I 88 in readiness for operation instantly upon closing contacts I54, I58, which remain open as long as the mercury is in engagement with the manometer contact I88, such engagement of the mercury maintaining coil I88 energized and contacts I88 and I88 are maintained closed.

Coil I22, however, is in a self-holding circuit, maintained by engagement ofarm I28 in contact with contact I88. As the mercury falls, along the manometer contacts I88, I88, until the mercury breaks engagement with the contact I86 I at the point H. This-break at H deenergizes coil I88 which automatically closes contacts I54, I58, thus instantly starting the clock motor I89, the circuit including coil I22 being self-holding until engagement of the mercury with contact I84 is broken at L, which deenergizes coil I22 and inclock motor I88 running duringthe fall of the mercury between the points H and L, a direct current being applied to motor-l88 immediately stopping the motor responsivel'y to the mercury falling below point L.

In the apparatus of the present invention, the I time of flow is determined, and the timing is automatic. Also, in the present case, the pressure varies from H to L, and consequently, the volume rate per second varies also from second to second.

At the initial stage, with mercury at H, let the pressure be P1. With mercury at point L, vlet the pressure be PL. The volume of air under pressure is a constant. Let this volume be V. From -the gas laws, as expansion takes place under flow, air leaves the system through the sample, so that the mass of air continually decreases. The gas law states that RV=nRT in which n is the number of mols of gas 'in volume V, R the gas constant, and T the absolute temperature.

Let m be the mols of air in volume V at the initial stage and n: at the final stage.

PiV=1l1RT and ' zw=mar Combining these Therefore if the volume of the metal system were to be determined, the volume or mass of air flowing through the sample can be calculated as mols, m-m), or as a portion of the volume of the metal system. The only variable determined in the test is the time required for it to pass through the test bed, which time depends on the fineness of. the sample.

constantly decreasing, throughout the period of the test. As related to the prior art, theime proved apparatus diifers in that a definite quantity of air is-made to pass through the sample,

under a pressure which varies between definite limits and the time elapsed is used to relate the varying flow rate with surface, the instrument being calibrated by testing samples of known surface therein determined. y

. It will be understood of course, that while air is illustrated and described herein as the penetrating fluid, other fluids may be used in a similar manner so long as they are inert to the particular powder being tested. Thus. a mobile oil might be used in the case of powders not reacted upon by water. Consequently air may be regarded as illustrative of a fluid that is found to be satisfactory in practice. 3

The apparatus described above may be rendered portable by mounting the-same on a truck,

, the table I I forming a platform which carries the testing mechanism which is mounted on a truck 2I2 provided with wheels 2i! and a handle 2 for pulling the truck to a desired location for use. Mounted on the truck 2I2 is the compressor 2I5 interconnected through a pressure tank 2I8 with the cleaning and testing instrumentalities and with a suction pump 2" which is connected through a suction tank 2I8 with the evacuating station for initially compacting the sample. The

apparatus therefore is made into a portable unit which can be transported readily around the slant to any desired location for .use.

Upon completion of the test, the tested sample must be removed. To do this the cylinder I8 is inverted under a nozzle 288 which receives compressed air from line 28I the air supply being controllable through a valve, 282. For holding the inverted cylinder for expulsion of the sample,

an abutment plate 288 is secured to the top of table II, as by bolts 284, into which plate is threaded a waste pipe 285 communicating with bag-288 for receiving the waste.

A bracket 28! which extends substantially vertically from the table likewise is bolted thereto by one of the bolts 288, the bracket 281 seating on the plate 283. At the top of the bracket is positioned a lever 288 which is pivoted at 288to the bracket 281, the lever 288 having a hole through it to accommodate the nozzle 288, and has a gasket 2I8.secured to it by screws 2I I. The lever 288 provides a convenient means for clamping the cylinder I8 in inverted position for blow ing out the compacted sample to clean the cylin-- der. While the illustrated embodiment of the invention herein specifically illustrated and described involves the use of a direct current for the relay coils and as a brake for stopping the timing motor, and an alternating current supply for running the motor. it will be apparent that the same sequence of control operations may beadapts itself readily for use as the timing motor.

What is claimed is: i

1. Testing apparatus for measuring surface of comminuted powders, which comprises, in combination, a supply of compressed air, achamber for holding a supply of compressed air under line pressure, mechanism for passing compressed air from the chamber through the sample, pressure-indicating means including a mercury' manometer connected to the compressed air line, control valves for controlling the supply of compressed air to the chamber, sample and pressureindicating means, a pair of elongated conductor members in the manometer one of which conductors is shorter than the other and disposed so that the shorter conductor is engaged last by the mercury in the manometer as the mercury rises under line pressure of compressed air, timing mechanism, first and second relay coils, a first direct current circuit including the first relay coil and the shorter manometer contact, whereby the mercury rising into engagement with the shorter contact causes the said relay coil to be energized, a second direct current circuit ininoperating direct current circuit, while being shiftable responsively to energizing the second relay coil into operative engagement with the alternating current circuit, contact members operable responsively to deenergizing the first relay coil incidently to disengagement of the mercury from the shorter manometer contact for closing the alternating current circuit as the mercury falls responsively to passing compressed air from the chamber through the sample, means for maintaining the second relay coil and alternating current circuit through the timing motor selfholding as the mercury continues to fall during passage of air through the sample until the mercury disen ages the longer manometer contact, thereby deenergizing the second coil and instantaneously returning the timing mechanism to direct current circuit. thereby applying direct current tothe mechanism as a dynamic brake to instantaneously stop the timing mechanism. which thereby automatically indicates the time of fall of the mercury between the manometer contacts,

I and means for indicating the said time in terms of surface values.

2. Testing apparatus for measuring surface of comminuted powders, which comprises, in combination. a supply of compressed air, a chamber for holding a quantity of compressed air under line pressure, mechanism for passin compressed air from the chamber through the sample. indi-- cating means'including a mercury manometer connected to the com ressed air line, control valves for controlling the sup ly of com ressed air to the chamber, sample and pressure-indicating means, a pair of s aced contact elements in the manometer. one of the contact elements being substantially shorter than the other, a supply of direct current. a first relay coil in circuit with the supply of direct current and the shorter for the said coil, a pair, of double contact'arms on the core adapted to make and break contact with a corresponding pair of double contacts, a

second relay coil is parallel with the first of the said relay coils, a supply of alternating current, timing mechanism adapted to be operated by the supply of'alternating current, contact elements operated by the second relay coil for controlling operation of the timing mechanism for shifting the timing mechanism between the supply of direct current and the supply of alternating current, a self-holding circuit for the second coil, whereby the second coil remains in circuit with the source of'direct current and with the contact elements of the manometer, a source of alternating potential, self-starting timing mechanism adapted to be operated by the alternating current, instrumentalities rendering the said timing mechanism operative during fall of mercury through a predetermined distance, and means for applying a dynamic brake to the timing mechanism for rendering the timing mechanism instantaneously out of operation responsively to completion of fall of the mercury through the said predetermined distance.

3. Testing apparatus for measuring surface of comminuted powders, which comprises, in combination, a supply of compressed air, a chamber for holding a supply of compressed air under line pressure, mechanism for passing compressed air from the chamber through a prepared sample of the powder, pressure-indicating means including a mercury manometer connected to the com pressed air line, control valves for controlling the supply of compressed air to the chamber, sample and pressure-indicating means, a plurality of contact members in the manometer, one of which members is an actuating contact member and another of the said members is a holding contact 40 member, the said members being spaced apart in direction of movement of mercury in the manometer, an actuating circuit including the actuating contact and a source of current, the actuating circuit becoming energized responsively to lifting of the mercury into engagement with the said initiating contact responsively to impressment of line pressures on the mercury, a second circuit energized responsively to energization of the ,actuating circuit, timing mechanism, a circuit for the timing mechanism rendered actuable by energizing the second circuit, a holding circuit for the said second circuit, the holding circuit including the holding manometer contact member,

cury manometer connected to the compressed air line, control valves for controlling the supply of compressed air to the chamber, sample'and presof the said contact elements, whereby the said sure-indicating means, first and second contact members in the-manometer, one of which members is an actuating contact member and the other of the said members is a holding member, the said members being spaced apart in direction of movement of mercury in the manometer, an

.actuatingcircuit including the actuating conresponsively to lifting tact and a source of current, the actuating eircuit becoming energized responsively to lifting of the mercury into engagement with the said in-' itiating contact member responsively to impressment of line pressures on the mercury, a second circuit energized responsively to energization of the actuating circuit, timing mechanism, a circuit for the timing mechanism rendered actuable by the energizing of the said second circuit, the holding circuit including the holding manometer contact member, means for closing instantaneously the circuit for the timing mechanism responsively to disengagement of the mercury from the actuating contact member responsively to the fall of the mercury incident to reduction of pressure as air is passed through the sample, the circuit for the timing mechanism thereby being closed responsively to deenergizing the actuating circuit while the holding circuit maintains the said-second circuit closed and energized as long as the mercury is in contact with the holding contact member in the manometer, and means for braking the timing mechanism to stop the same responsively to disengagement of the mercury with the holding contact member.

5. Testing apparatus for measuring total surface in a bed of comminuted powders, which comprises, in combination, a source of compressed air, a chamber for holding a supply of compressed air received from the'source thereof, means for passing compressed air from the chamber through the sample, pressure indicating means including a mercury manometer connected to the compressed air line, control valves for controlling the supply of compressed air to the chamber. sample and pressure-indicating means, first and second contact members in the manometer, one of which members is an initiating contact member and the other of the said members is a holding contact member, the said members being spaced apart in direction of movement of mercury in the manometer, an actuating circuit including the actuating contact, and a source of current, the actuating circuit becoming energized of the mercury into engagement with the said initiating contact member responsively to impressment of line pressures on the mercury, a second circuit energized responsively to energization of the actuating circuit, timing mechanism, a circuit for the timing mechanism rendered actuable by the energizing of the said second circuit, a holding circuit for the said second circuit, the holding circuit including the holding manometer contact member, means for closing instantaneously the circuit for the timing mechanism responsively to disengagement of the mercury member responsively to fall of the mercury incident to reduction of pressure as air is passed through the sample, the circuit for the timing mechanism thereby being closed responsively to deenergizing the actuating circuit while the holding circuit maintains the said second circuit closed and energized as long as the mercury is in contact with the holding contact member in the manometer, means for braking the timing mechto disengagement of ,duction of pressure in same immediately responsively the mercury withthe holding contact member, whereby the timing mechanism indicates the time required for the mercury to fall between the two manometer contacts, thereby indicating time of flow of standard volume of air through the sample, and means for indicating the said time in terms of surface.

6. Testing. apparatus formeasuring surface of comminuted powders, which comprises, in combination, a container for receiving a known amount of a prepared sample of the powder to be tested, a supply of compressed air, dicating line pressure of the compressed air, a chamber for holding a supply of compressed air under line pressure, mechanism for passing compressed air-from the chamber throughthe powder container in the said container, indicating anism to stop the means for measuring line pressure, a first control valve for controlling the supply of compressed air to the chamber and pressure-indicating means, a second valve for controlling flow of compressed air to the sample, .whereby, upon closing of the first valve and opening of the second valve, air from the chamber passes through the sample with corresponding continuous rethe pressure-indicating means, and timing mechanism operated by the pressure-indicating means for indicating time of passage of a constant volume of air through the sample and surface measurements. '7. Testing apparatus comminuted powders, which comprises, in combination, a source of compressed air, indicating line pressure of the compressed air, a chamber for holding a supply of compressed air from the source under line pressure, mechanism for passing compressed air from the chamber through the sample, indicating means including a mercury manometer'connected to the compressed air line, control valves for controlling the supply of compressed air to the chamber, sample contained therein, and pressure-indicating means, a pair of vertically spaced-apart contact elements in the manometer, and timing mechanism adapted to be operated responsivelyto fall of mercury in the manometer through the 'space between the said contact elements, and

means for converting the resulting time of fall into surface measurements.

8. A method of testing powdered materials for determining total surface thereof. which com- I prises introducing a weighed sample of the pew-- from the actuating contact der into a testing receiver therefor, evacuating entrained air from the sample'and correspondingly partially compacting the sample, further compressing the sample into a standard volume, passing a measured volume of compressed air through the compressed. sample, measuring a standard volume of air passing through the sample, and measuring in terms of surface, the time required for the volume of air to pass through the sample.

ROBERT E. mm

means for infor translating the said time into for measuring surface of. 

